Conventionally, handheld process calibration equipment showed the primary variable being tested. As an example, a conventional 4–20 mA calibrator shows the current output or reading. This may be scaled in mA or percentage of the 4–20 mA span.
Moreover, conventional calibrators may show error enunciators such as “overload,” “over-current,” “ERROR” etc. While these enunciators may indicate that there is an error, the conventional calibrators fail to supply sufficient information to determine the source of the error.
For example, with conventional portable calibration equipment when the calibrator shows an “ERROR,” the user would have to pull out a number of test instruments to determine the actual source of the error. These instruments would typically have to be carried into the “field.” Thus, the user may have to carry the device, and all the accompanying instruments, long distances, possibly up ladders, or to very remote locations. Usually, the accompanying equipment includes a digital multi-meter, power supplies, decade boxes, etc. These devices would have to be hooked up with or in place of the conventional calibrator to determine the actual error source; i.e., the circuit had no supply voltage, the circuit had high impedance, or a component was leaking current.
In addition to additional equipment, these troubleshooting connections may be complicated. Moreover, the troubleshooting routines typically have difficulty monitoring “dynamic” changes within the “normal” operating conditions, as well as, fail to provide any “logging” capabilities.
Conventionally, transient out of normal conditions are monitored manually one variable at a time or the user has to watch for the error condition to occur. This is very time consuming and error prone.
To better understand the problems associated with conventional calibrators, a discussion of FIGS. 1 and 2 will be provided below.
As illustrated in FIG. 1, a process loop includes a calibrated digital control source 10 connected to a field transmitter 20 through communication channel 25, in this example, a pair of wires. As shown, a 20 mA signal is sent from the calibrated digital control source 10 to a field transmitter 20 for calibration purposes, but due to a remote fault or corroded connections, the amperage amplitude of the signal received by the field transmitter 20 is reduced, by a leakage current iLeakage, shown as flowing through a leakage resistance. In response thereof, the field transmitter 20 produces a return signal for the calibrated digital control source 10 wherein this return signal has amperage amplitude of 20 mA minus ileakage. The return signal is combined with the leakage current, iLeakage, to create a signal having amperage amplitude of 20 mA. The actual amperage amplitude of the signal received by the calibrated digital control source 10 is shown on display 11. Thus, in this system, an undetected calibration error is realized because the actual amperage amplitude of the signal received by the field transmitter 20 is 20 mA minus iLeakage, but the actual amperage amplitude of the signal received by the calibrated digital control source 10 is 20 mA, as shown on display 11. Thus, the operator is unaware that a fault has occurred.
FIG. 2 illustrates another example of this problem. As illustrated in FIG. 2, a process loop includes a portable calibrated digital control source 30 connected to a field transmitter 20 through communication channel 25, in this example, a pair of wires. As shown, a 20 mA signal is sent from the portable calibrated digital control source 30 to a field transmitter 20 for calibration purposes, but due to a remote fault or corroded connections, the amperage amplitude of the signal received by the field transmitter 20 is reduced, by a leakage current iLeakage, shown as flowing through a leakage resistance. In response thereof, the field transmitter 20 produces a return signal for the portable calibrated digital control source 30 wherein this return signal has amperage amplitude of 20 mA minus iLeakage. The return signal is combined with the leakage current, iLeakage, to create a signal having amperage amplitude of 20 mA. The actual amperage amplitude of the signal received by the portable calibrated digital control source 30 is shown on display 31. Thus, in this system, an undetected calibration error is realized because the actual amperage amplitude of the signal received by the field transmitter 20 is 20 mA minus iLeakage, but the actual amperage amplitude of the signal received by the portable calibrated digital control source 30 is 20 mA, as shown on display 31. Thus, the operator is unaware that a fault has occurred.
Therefore, it is desirable to provide a device that is capable of monitoring and displaying additional information (variables) in one or more concise screens. It is also desirable to provide a device that is capable of indicating on the display the most likely cause of error as compared to normal operating conditions, more specifically, capable of highlighting the “non-primary” variable(s) that is out of the normal range or condition, thereby allowing the user on one screen to identify and troubleshoot.
It is further desirable to provide a device that is capable of easily monitoring “dynamic” changes within the “normal” operating conditions. Furthermore, it is also desirable to provide a device that is capable of logging conditions to enable monitoring for transient out of normal conditions. In addition, it is also desirable to provide a device that is capable of testing with the lowest common denominator of connections required.
Moreover, it is also desirable to provide a device that is capable of eliminating the need for digital multi-meters in the industry specific calibration processes and supply such information without requiring several different connection schemes to acquire if at all.
Lastly, it is also desirable to provide a calibration capable of producing the unknown variables of Current, Voltage (AC, DC), Resistance, Capacitance and Inductance so as to enable concurrent measurement and display of the various variables without requiring disconnection and reconnection when, for example, a current measurement is required and a voltage reading is required, thereby allowing the diagnostics of multiple variables with a single connection scheme.